[sdiy] looking for schematic for dual vco

[Scott Bernardi]

Let's make sure what you're asking is what you really mean.  The term "mix"
usually refers to a simple summation of multiple signals. The mixed output
will sound like two separate tones if the frequencies of the input signals
are far apart, and will sound like tonal variations if they are close
together.  You could, for instance, mix the outputs of a single VCO to do
this.
If the frequencies are just slightly different, you get a pleasing audio
effect called "beating", where the phases add and cancel over time, varying
the amplitude.  This is what chorus circuits simulate.
You might want a general purpose mixer module to mix multiple signals,
rather than a dedicated circuit to mix just the two VCO's. And yes, it's
based on an opamp in what is called a "summing amplifier" configuration.
Here's a schematic for a general purpose mixer module:
http://members.home.net/sbernardi/elec/mixer.html

Another way to combine two VCO signals is to multiply them (rather than
sum). This is done by a Ring Modulator circuit.
http://members.home.net/sbernardi/elec/og2/og2_ringmod.html

And yet another way is to "crossfade". This is where you smoothly transition
from one waveform into another, usually under voltage control. Jurgen
Haible's Interpolating Scanner circuit is a good example of this:
http://home.t-online.de/home/jhaible/jh_ipscan.html

Now, as far as a dual VCO, you said you don't like the CEM3340, but here's
one based on the CEM3374 dual VCO chip (available from Synthesis Technology
for $15).
http://members.home.net/sbernardi/elec/og2/og2_cem3374.html

cacofone wrote:

> Hello, looking for a current (doesn't use CEM3340) Dual VCO, where I can
> mix the VCO's (i.e. Pulse/triangle etc)
>
> Or, if I've got two VCO's, how do I mix the two? With an op-amp?
>
> looking for more details...
>
> nKode / Pulse 8 / cacofone [aim:jkerseyVCSO]
> Good Time Tribe / http://www.goodtimetribe.com
> Dallas Regional Electronic Artists And Musicians
> http://www.mp3.com/stations/D-R-E-A-M
> http://www.mp3.com/nkode / http://www.mp3.com/cacofone /
> http://www.mp3.com/pulse8

--
Scott Bernardi
sbernardi at home.net